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RST Instruments Ltd. 11545 Kingston St., Maple Ridge, B.C. Canada V2X 0Z5 Tel: (604) 540-1100 Fax: (604) 540-1005 Email: [email protected] Website: www.rstinstruments.com

VW Liquid Settlement System

Instruction Manual

VW Liquid Settlement System Instruction Manual

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Although all efforts have been made to ensure the accuracy and completeness of the information contained in this document, RST Instruments reserves the right to change the information at any time and assumes no liability for its accuracy.

Product: VW Liquid Settlement System Instruction Manual

Document number: SSM0018D

Revision: D

Date: January 16, 2015


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Table of Contents

1 INTRODUCTION ................................................................................................................................... 1

2 INSTALLATION ..................................................................................................................................... 4

3 RESERVOIR ASSEMBLY INSTRUCTIONS ......................................................................................... 6

4 OPERATION .......................................................................................................................................... 8

4.1 CALCULATION OF DATA WITHOUT BAROMETER .............................................................................................. 9 4.2 CALCULATION OF DATA WITH BAROMETER .................................................................................................... 9

5 TROUBLESHOOTING & MAINTENANCE ......................................................................................... 10

APPENDIX A ............................................................................................................................................... 11

APPENDIX B ............................................................................................................................................... 12

Table of Illustrations Figure 1: Typical installation of VW Settlement System ............................................................. 1 Figure 2: Typical layout of Reservoir and VW Transducer ......................................................... 2 Figure 3: Various configurations of Reservoir and VW Transducer ............................................ 3 Figure 4: Reservoir mounting ..................................................................................................... 6 Figure 5: Removing the 6” extension pipes & caps .................................................................... 7 Figure 6: Filling the female quick connects with de-sired solution .............................................. 7 Figure 7: Monitoring settlement or heave ................................................................................... 8 Table 1: Thermistor Resistance (Ω) versus Temperature (°C) ..................................................11


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1 INTRODUCTION Liquid Settlement Systems are used in many situations, such as:

preload consolidation monitoring

construction control of embankments, and tills

subsidence monitoring

The RST VW Liquid Settlement System monitors settlement or heave, by measuring any changes in elevation between a reservoir and a settlement plate as shown in Figure 1. The liquid reservoir is mounted, ideally in a stable location (i.e. not subjected to any settlement), at a higher elevation relative to the settlement plate. As the plate settles, the liquid pressure at the settlement plate increases and is measured by the vibrating wire sensor.

Figure 1: Typical installation of VW Settlement System

Typical VW Liquid Settlement System consists of an array of vibrating wire sensors connected to fluid-filled tubes branching from the manifold. Each branch contains a sensor that is installed at a specific location. Each sensor contains a thermistor for temperature measurement, and gas discharge tubes for lightning protection. The system uses de-aired antifreeze solution to prevent algae growth and freezing. Furthermore, the system uses two liquid lines so that it may be flushed in order to remove air bubbles from the system. Settlement is measured relative to the initial readings taken during installation. Changes in atmospheric conditions and fluid level evaporation are compensated for by an additional vibrating wire sensor located at the manifold. Settlement of the reservoir can be corrected from manual survey data.


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Figure 2: Typical layout of Reservoir and VW Transducer

Different system options are shown in the figure below. The system may have any number of positions, and different types of tubing.

INSTRUMENTS

RESERVOIR

MANIFOLD PORTS

SENSOR

FLUID FILLEDTUBES


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Figure 3: Various configurations of Reservoir and VW Transducer


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2 INSTALLATION Liquid settlement systems are shipped pre-filled, tested, calibrated, and ready to install. Generally, 5% additional tubing should be used to accommodate settlement.

It is critical that the settlement as shown in Figure 1 be within the anticipated range

of the sensor. This system uses the 10psi sensor and thus the maximum

settlement is 6.57m. For example, if the site conditions require that the initial

installation height be 2.57m, the anchor plate can settle a maximum of 4m before

the sensor is over pressurized and possibly becomes permanently damaged.

Typical installations in fill entail:

1. Embedding the settlement plate and sensor at the point to be monitored:

A smooth, flat-bottomed excavation should be made in the fill for placement of the plate. This should be about 6 to 12 inches deep. The sensor and plate assembly should be placed in the excavation and surrounded by fine sand to a level at least 6 inches above the sensor and tamped in place.

2. Running the cable and tubing in a trench up to the reservoir:

As the relative density of the fluid in the liquid lines changes with temperature, the interconnecting tubing should be buried and the system maintained at a constant temperature. Any additional tube at the reservoir end should be coiled and buried, with only the minimum length of tubing required above ground leading to the reservoir. If the cables are not buried, they should be adequately supported to prevent undulations and protected from sunlight and rapid temperature fluctuations with insulation.

When running the cable and tubing to the readout location, localized high areas should be avoided and in no case should any part of the tubing be above the reservoir elevation. The cable and tubing should be placed in a trench (6 to 12 inches deep) that runs to the readout location, and surrounded with fine grain material which should be subsequently compacted. Prior to back filling the trench, it is recommend that the system be tested by making the necessary connections (see subsequent steps) and progressively raising the reservoir upwards, to simulate settlement in the system, while verifying with a vibrating wire readout that the system is operating correctly. Large angular rocks must not rest directly on the cables. Furthermore, the migration of water along the trench may be prevented by filling with bentonite at intervals. Compaction of succeeding lifts over the sensor and tubing can now proceed in the normal manner.

3. Installing the reservoir:

The reservoir should be installed in a location that is on stable ground away from the area of anticipated settlement or one that can be periodically checked by survey so that it can provide a fixed reference level. The computations for settlement are based on the difference in elevation between the reservoir and the sensor, and therefore the reservoir fluid elevation must be known. The reservoir should be filled up to the overflow fitting (use de-aired solution of 50% distilled water and 50% ethylene glycol antifreeze) before the instrument is attached and should be topped up if necessary before taking readings. A few drops of light oil added through the top of the reservoir will slow down evaporation from the liquid surface.


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4. Connecting the tubes and cable from the sensor to the junction box:

There are two tubes so that the system may be flushed if any air bubbles ever contaminate the system. The female quick connects should be topped up with liquid in order to avoid introducing air bubbles into the system before simultaneously snapping them into the reservoir connections.

The cable runs through the cable gland and the wires are connected to the terminal block as per the wiring diagram on the inner enclosure panel (generally, the black and red colors represent the vibrating wire element, the green and white colors represent the thermistor, and the last color represents the cable shield).

5. Acquiring initial readings:

The reservoir should be filled up to the overflow point to serve as a quick visual check on any future fluctuations due to temperature, pressure, evaporation or leakage. Also, the ambient temperature should be recorded.

Connect a vibrating wire readout to the junction box by matching the colors of the connectors and record the initial reading. Also, record the initial sensor temperature (if the readout does not display the sensor temperature, then the temperature may be obtained by measuring the resistance between the green and white banana jacks and using the conversion formula in the appendix). These measurements will serve as the reference or zero measurements for the future, and thus it is necessary to double check that they are stable.


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3 RESERVOIR Assembly Instructions 1. Mount Reservoir Assembly. Make sure the Assembly is level using a spirit level.

Figure 4: Reservoir mounting

2. Ensure the site is ready for installation as per the site engineer’s instructions. This includes:

1. An inclined, evenly graded, surveyed trench for laying the sensor leads back to the manifold.

(Trench depth must accommodate a 12”(300mm) bed of, packed, Select Backfill).

2. Enough sand to provide a 1”(25mm) thick leveling base for each cell.

3. Enough Select Backfill to provide a 12”(300mm) protective barrier for the Cell and its leads, from the Regular Backfill.

3. Survey in each sensor at its site specific Reference location and level. 4. Survey in the Reference Level at the manifold location. 5. Fill the reservoir to the level indicated by the red line on the outer surface of the reservoir with the

de-aired solution provided. 6. Remove both 6” extension pipes and caps in the reservoir. (Liquid is pre-filled in the manifold to

ensure no air is trapped in the system.)


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Figure 5: Removing the 6” extension pipes & caps

7. Fill each of the female quick connects with de-aired solution. Attach both tubes of each sensor to

the manifold at the same time.

Figure 6: Filling the female quick connects with de-sired solution

8. Fill the end of the female Quick Connect, on the Barometric VW Transducer, if installed, with fluid

and then connect it to the Manifold. 9. Top up the reservoir level if required and add a couple drops of mineral oil to the reservoir to

prevent evaporation. 10. Make electrical connections to a readout/datalogger (RST VW-2106) and take the initial readings.


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Note: If air is suspected in the lines then contact RST Instruments for further instructions.

4 OPERATION After the installation, the measurements may be obtained by using the RST Vibrating Wire Readouts. Connect the readout to the junction box by matching the colors of the connectors. The black and red colors carry the frequency signal that is proportional to the pressure. The green and white colors are connected to the thermistor.

Having recorded the initial reading and temperature after installation, the zero reading is now established and all subsequent data can be referred to these numbers. Use the initial count reading as R0 and the initial temperature recorded as T0. Refer to the calibration sheets for the appropriate calibration and thermal factors for each system. Use the following formula to determine settlement.

Rm

Rm

RESERVOIR

SENSORBAROMETER SENSOR

Settlement

Figure 7: Monitoring settlement or heave


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4.1 CALCULATION OF DATA WITHOUT BAROMETER

)(*)(*, cici TTTkLLCFzSettlement

Where:

CF = Calibration Factor (from Calibration Sheet)

LI = Initial Readout Box reading

Lc = Current Readout Box reading

Tk = Thermal Factor (from Calibration Sheet)

Ti =Initial Temperature.

Tc =Current Temperature

For example, if the initial readings at installation were 7905 Hz2/1000 and 17°C, and the current

readings are 7530 Hz2/1000 and 15°C (and the calibration sheet shows -0.0015936 m/B for CF

and -0.0043 m/(°C) for Tk, a sample calibration sheet is included in the appendix), then the plate has settled a distance of 0.589m:

mmmCCmbmz o 589.0009.0598.0)1517(*)/0043.0()75307905(*)/0015936.0(

From the above sample calculation, it can be seen that generally the temperature effects are small, which is especially true for buried cable.

4.2 CALCULATION OF DATA WITH BAROMETER

)(*0953.0)(*)(*, cicici BBTTTkLLCFzSettlement

Where:

CF = Calibration Factor (from Calibration Sheet)

LI = Initial Readout Box reading

Lc = Current Readout Box reading

Tk = Thermal Factor (from Calibration Sheet)

Ti =Initial Temperature.

Tc =Current Temperature

Bi= Initial Barometric pressure (at installation)

Bc = Current Barometric pressure in kPa (at time of reading)


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5 TROUBLESHOOTING & MAINTENANCE If the readings appear faulty (i.e. unstable, fluctuating, or simply unrelated to physical phenomena), then several checks should be made. First, check that the readout is functioning correctly. A continuity check of the sensor should also be performed. The resistance between the gauge leads (Red and Black wires) should be approximately 180Ω. The resistance between the thermistor leads (Green and White wires) should be approximately 3kΩ at room temperature. It may be important to add the cable resistance to these numbers (note that 22 AWG stranded copper leads have resistance

of approximately 48.5/km).

Second, check that the liquid level in the reservoir is at the overflow point. If the liquid level dropped significantly, then there is most likely a leak in the system. Also, visually check for air bubbles or plugged lines in the system, in which case it will be necessary to flush the system (contact RST Instruments for assistance).

Unstable readings may also result from electrical noise such as nearby power lines or electrical equipment because the vibrating wire signal is very susceptible to frequency noise. If possible, the readings should be taken when the equipment is not operating; otherwise, it may be necessary to move away from the noise.

The vibrating wire sensor is completely sealed and does not require maintenance. In fact, only the junction box and the connecting tubing and cable require minimal attention. Approximately every three months, visually examine the reservoir level and add liquid if necessary up to the overflow tube. Also, check that there are no leaks and air bubbles in the tubing, and that the tubing is not plugged. Furthermore, check that the electrical connections are not corroded.


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APPENDIX A

The following equation may be used to convert the measured thermistor resistance R (Ω) to temperature T (°C).

2.273))(ln(*10*019.1)ln(*10*369.210*4051.1

13743

RRT

Alternatively, the values may be looked up directly in Table 1.

Table 1: Thermistor Resistance (Ω) versus Temperature (°C)

Ohms Temp Ohms Temp Ohms Temp Ohms Temp Ohms Temp 201.1K -50 16.60K -10 2417 +30 525.4 +70 153.2 +110 187.3K -49 15.72K -9 2317 31 507.8 71 149.0 111 174.5K -48 14.90K -8 2221 32 490.9 72 145.0 112 162.7K -47 14.12K -7 2130 33 474.7 73 141.11 113 151.7K -46 13.39K -6 2042 34 459.0 74 137.2 114 141.6K -45 12.70K -5 1959 35 444.0 75 133.6 115 132.2K -44 12.05K -4 1880 36 429.5 76 130.0 116 123.5K -43 11.44K -3 1805 37 415.6 77 126.5 117 115.4K -42 10.86K -2 1733 38 402.2 78 123.2 118 107.9K -41 10.31K -1 1664 39 389.3 79 119.9 119 101.0K -40 9796 0 1598 40 376.9 80 116.8 120 94.48K -39 9310 +1 1535 41 364.9 81 113.8 121 88.46K -38 8851 2 1475 42 353.4 82 110.8 122 82.87K -37 8417 3 1418 43 342..2 83 107.9 123 77.99K -36 8006 4 1363 44 331.5 84 105.2 124 72.81K -35 7618 5 1310 45 321.2 85 102.5 125 68.30K -35 7252 6 1260 46 311.3 86 99.9 126 64.09K -33 6905 7 1212 47 301.7 87 97.3 127 60.17K -32 6576 8 1167 48 282.4 88 94.9 128 56.51K -31 6265 9 1123 49 283.5 89 92.5 129 53.10K -30 5971 10 1081 50 274.9 90 90.2 130 49.91K -29 56.92 11 1040 51 266.6 91 87.9 131 46.94K -28 5427 12 1002 52 258.6 92 85.7 132 44.16K -27 5177 13 965. 53 250.9 93 83.6 134 39.13K -25 4714 15 895.8 55 236.2 95 79.6 135 36.86K -24 4500 16 863.3 56 229.3 96 77.6 136 34.73K -23 4297 17 832.2 57 222.6 97 75.8 137 32.74K -22 4105 18 802.3 58 216.1 98 73.9 138 30.87K -21 3922 19 773.7 59 209.8 99 72.2 139 29.13K -20 3748 20 746.3 60 203.8 100 70.4 140 27.49K -19 3583 21 719.9 61 197.9 101 68.8 141 25.95K -18 3426 22 694.7 62 192.2 102 67.1 142 24.51K -17 3277 23 670.4 63 186.8 103 65.5 143 23.16K -16 3135 24 647.1 64 181.5 104 64.0 144 21.89K -15 3000 25 624.7 65 176.4 105 62.5 145 20.70K -14 2872 26 603.3 66 171.4 106 61.1 146 19.58K -13 2750 27 582.6 67 166.7 107 59.6 147 18.52K -12 2633 28 562.8 68 162.0 108 58.3 148 17.53K -11 2523 29 543.7 69 157.6 109 56.8 149

55.6 150


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APPENDIX B

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